Lecture Transformation

8/18/2019 Lecture Transformation

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Digital Image Processing

Gray Level Enhancement

Dr. Muhammad Jehanzeb


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Gray level enhancement

Some of the simplest, yet most useful,

image processing operations involve theadjustment of brightness, contrast or color in

an image. This operation is called contrast

enhancement.


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Gray level enhancement

• common reason for manipulating theseattributes is the need to compensate fordifficulties in image ac!uisition.

• "ontrast enhancement aims to improve animage such that the content of an image

become visually more pleasing.


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dar# image


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n enhanced image


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There are several techni!ues in enhancingthe contrast of digital image such ashistogram stretch, histogram e!uali$ationand adaptive contrast enhancement.

%istogram e!uali$ation is a popular

techni!ue for improving the appearance of a poor image.


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Its function is similar to that of a histogram

stretch but often provides more visually pleasing results across &ider range of

images.


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%istogram '!uali$ation lgorithm

%istogram '!uali$ation is a techni!ue &here the

histogram of the resultant image is as flat as

possible.

(ith histogram stretching the overall shape of the

histogram remains the same.

The theoretical basis for histogram e!uali$ation

involves probability theory, &here the histogram is

treated as the probability distribution of the gray

levels.


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%istogram '!uali$ation lgorithm

The histogram e!uali$ation process for digital image

consists of four steps)

i. *ind the running sum of the histogram valuesii. +ormali$e the values from step i- by dividing by the

total number of piels

iii. /ultiply the values from step ii- by maimum gray

level value and round

iv. /ap the gray level values to the results from step iii-‑

using a one to one correspondence‑ ‑


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Example: Given a 0 bits1image, so the possible range

of values is 2 to 3. Suppose the image has the

follo&ing histogram)

%istogram of image


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%istogram of original image


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steps to find the histogram1e!uali$ed values.


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In order to get the histogram e!uali$ed‑

image, all piels in the original image &ith

gray level 2 are set to 4, values of 4 are set 5,5 set 6, 6 set to 6, and so on

Table sho&s the histogram of the

histogram e!uali$ed image.‑


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%istogram of the histogram1e!uali$ed image


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%istogram of histogram1e!uali$ed image

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